MONTREAL — Some people dabble in painting, others have a passion for golf, but Bernard Trépanier says his “hobby” of choice was politics. And for a diversion, it turned out to be very lucrative.

Testifying Tuesday before Quebec’s public inquiry into corruption, the former political organizer and bagman said he caught the bug in 1983, volunteering for the federal Progressive Conservatives.

When the party swept to power in 1984 under Brian Mulroney, Mr. Trépanier went to work in Ottawa as a political aide to a series of transport ministers. After three years, he returned to Quebec, where he worked in waste management and became a hired gun organizing municipal campaigns.

The appearance by the man nicknamed Mr. Three Percent was one of the most anticipated since the commission began sitting last spring. Previous witnesses have identified the former director of finance for Union Montreal party as key to a collusion scheme that funnelled 3% of the value of municipal engineering contracts into party coffers.

Most of the testimony Tuesday dealt with the period before he was hired by Union Montreal, the party of former mayor Gérald Tremblay, in 2004, but there were glimpses into the sausage-making side of politics.

Mr. Trépanier, 74, described how he became an organizer for hire, a “false volunteer” who helped candidates win election in municipalities on and around the island of Montreal. He said he was paid, usually in cash, for his work in what are called turnkey elections — legal or engineering firms would bankroll a party’s campaign with the understanding they would land work if their team won.

He was not always a political mercenary. When he worked on the election campaigns of Frank Zampino, who would serve as Mr. Tremblay’s right-hand man on city council, he said he was not paid.

“A friend’s a friend. I never asked for anything from Mr. Zampino,” he said describing the campaign as a family affair.

More valuable than the cash occasionally slipped under the table were the contacts Mr. Trépanier developed in various administrations. He formed a consulting firm called Bermax — “my first name is Bernard, so it’s Bernard to the max,” he explained — and worked as an unofficial lobbyist.

“I was simply the door-opener. I am not an urban planner. I’m not a specialist in communications,” he said. “I always learned that when you want to get from point A to point B as quickly as possible, it takes contacts.”

Commission counsel Denis Gallant tabled evidence that from 2002 to 2010, Mr. Trépanier and Bermax made more than $100,000 a year from a single client, the engineering firm Dessau Inc. Part of this overlapped with when he was drawing an $82,000 salary from Union Montreal.

Mr. Trépanier testified that the payments were all a result of his work locating a specialist who aided Dessau in qualifying as a bidder for work with the Montreal airport authority.

‘I always learned that when you want to get from point A to point B as quickly as possible, it takes contacts’

Mr. Gallant and the two commissioners expressed skepticism that the firm would pay so much — a total of $906,000 — for work that was essentially that of a middleman.

“Did you defraud Dessau?” Mr. Gallant asked. “I did not defraud Dessau,” Mr. Trépanier replied, but he struggled to explain what he had done to earn the payments.

Late Tuesday, Dessau issued a news release saying the firm’s president and senior management learned of the payments to Mr. Trépanier last week when its vice-president, Rosaire Sauriol, testified before the commission. At the commission’s request, the firm checked its records, discovered the extent of the payments and handed the information over to the commission on Monday, the release said.

“Mr. Rosaire Sauriol resigned from his position as principal vice-president the same day,” it said.

Mr. Trépanier, who quit his job with Union Montreal in 2006, is facing five charges including fraud and breach of trust in relation to the sale of municipal land for a real-estate development known as Faubourg Contrecoeur. His testimony resumes Wednesday.

Mr. Zampino, who quit politics in 2008, is charged in the same case. He was hired by Dessau but resigned amid controversy in 2009 over a water-meter contract awarded to the firm while Mr. Zampino was executive committee chairman.